1. Field of the Invention
This invention relates to remote sensing and, more particularly, to active remote sensing and specifically active polarimetery.
2. Description of Related Art
Active remote sensing may be conceptualized as viewing radiation reflected and/or emitted from a certain location. Active remote sensing typically utilizes one or more sources of radiation (e.g., infrared, visible, or ultraviolet light) to illuminate a target area while measuring the reflected, scattered and/or emitted radiation at one or more detectors. Where the detector(s) in a sensor produce or construct a two-dimensional image of the target that includes a number of pixels, such a sensor is typically referred to as an “imaging” sensor. Such remote sensing may be performed from a moving platform or from a stationary location, each of which may be spatially remote from the target area.
One type of remote sensor, such as a spectrometer, may detect radiation in one or more wavelength regions. Another type of remote sensor, a polarimeter, may detect radiation at one or more polarizations (which may also be referred to as “colors” to denote their different behavior even though the different polarizations may not be visually perceived in different wavelength regions). For imaging polarimeters, it is typically desirable to produce images at two or more different polarizations to enable detection of specific objects/areas within a target field of view that reflect/scatter/emit radiation differently under different polarizations.
One scheme for generating images at different polarizations is to use multiple detectors with different polarizing optics to separately image one target. In such a scheme, however, image mis-registration, where corresponding pixels in different detectors do not spatially correspond to the same location on the target, becomes troublesome. Other schemes have been proposed to use a single detector (e.g., focal plane array) and to separate the differently polarized images into, for example, quadrants or sets of adjacent pixels within the detector. These schemes, however, also suffer the mis-registration problem to some degree.
Thus, there is a need in the art to perform active polarization imaging while avoiding mis-registration among images at different polarizations.